check that the amp is working both channels, use a point before the relay to test.
if the amp is working ok (with a small DC offset <50mV) then its likely to be the protection circuit, particularly, the caps around the chip go bad. try the 100uF one first.

May be you dlike to study them uncle charly ....but my advice is DONT ....!!!!

These amps are very very easy to fail not from design but mostly from construction details and cheap quality .
Then on the other hand most models i worked from interM destroyed my speakers if operate them close to 100% or first clip ....